Read the passage carefully and answer the questions.

Amines are considered to be derivatives of ammonia obtained by replacement of hydrogen atoms with alkyl or aryl groups. They are usually prepared from nitro compounds, halides, amides, imides etc. The presence of hydrogen bonding influences its physical properties. In alkylamines, a combination of electron releasing steric and hydrogen bonding factors influences the stability of substituted ammonium cations in protic polar solvents and thus affects the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia which is more basic than water. Primary and secondary amines are engaged in intermolecular association due to hydrogen bonding. This intermolecular association is more in primary amines than in secondary amines. Tertiary amines do not have intermoleulcar association due to the absence of hydrogen atom available for hydrogen bonding. Thus, the boiling point of amines depends on hydrogen bonding. In aromatic amines, electron releasing and withdrawing groups increase and decrease their basic character. Aryl diazonium salts usually obtained from arylamine undergo replacement of the diazonium group with a variety of nucleophile. Their coupling reaction of aryl diazonium salts with phenol or arylamine results in formation of dyes.

Which of the following compounds will not undergo azo coupling with benzene diazonium chloride?

Nitrobenzene

The correct answer is Option (4) → Nitrobenzene

Azo coupling is an electrophilic aromatic substitution where an aromatic compound rich in electron density reacts with a diazonium salt to form an $-\text{N}=\text{N}-$ (azo) dye.

It requires a strongly activated aromatic ring (electron-donating group).

Rule to Remember

• Electron-donating groups $\rightarrow$ Azo coupling possible
• Strong electron-withdrawing groups ($-\text{NO}_2$, $-\text{COOH}$, $-\text{SO}_3\text{H}$) $\rightarrow$ No azo coupling

Explanation of Each Option

Option 1: Anisole ($-\text{OCH}_3$ group)

Methoxy is a strong electron-donating group ($+M$ effect). It activates the ring, especially at the para position. Hence anisole readily undergoes azo coupling.

Option 2: Phenol ($-\text{OH}$ group)

The hydroxyl group strongly activates the ring via resonance. Phenol is one of the most common compounds used in azo dye formation.

Option 3: Aniline ($-\text{NH}_2$ group)

Amino group donates electron density strongly. Aniline easily couples with diazonium salts, usually in mildly acidic medium, giving colored azo compounds.

Option 4: Nitrobenzene ($-\text{NO}_2$ group)

Nitro group is a strong electron-withdrawing group ($-M, -I$ effect). It deactivates the ring toward electrophilic substitution, so azo coupling does not occur.